most non-technical people treat urls mostly as blobs (which doesn't mean they don't understand it's consisted of parts, but that's irrelevant)

so the URL field is mostly operating one urls as a while

that's why if you click on it in difference to normal text it will always select the whole url, because most times most people will either copy that url or fully replace it

similar "Past and Go" also operates as the url as a whole, not text segments. So it pasts the new url to where the old url was and "goes" to the new website

additionally if you don't just replace an url but edit it a "do this edit and directly go without giving me a chance to double check it" functionality doesn't really have any reason to exist as its way too niche and people who do that likely anyway use keyboard shortkuts instead of the context menu

sure there probably could be a better name e.g. "Replace Tab and Go". Or they could not show it if you don't have all text selected.

But "Past and Go" isn't a description of functionality anymore but has become something like a slogan or special term. So neither renaming it nor changing behavior is really acceptable from a UX POV.